Delamination In Composites Research Articles

A novel implementation of the cohesive zone model for the fatigue propagation of delamination in composites using a sequential static fatigue algorithm

Composite materials are particularly exposed to delamination under fatigue loading conditions, which can significantly compromise their structural integrity. The ability to accurately and efficiently estimate the progression of delamination under fatigue is crucial for enhancing the safety and reliability of lightweight composite structures. The aim of this paper is to implement the cohesive elements formulation in a Sequential Static Fatigue (SSF) algorithm named C-SSF. The C-SSF algorithm simulates delamination propagation under fatigue loading by conducting a series of sequential static simulations. The accuracy of the C-SSF method is validated by comparing its results with experimental data from two published case studies. The results demonstrate that this approach can effectively simulate delamination growth under fatigue loading. Compared to a similar approach based on the Virtual Crack Closure Technique (VCCT), the C-SSF algorithm provided superior accuracy, especially when large and curved delamination fronts were involved. The C-SSF method proved its capability to simulate propagation of delamination in composite structures, making it a valuable tool for modelling the fatigue behaviour of other similar structures.

Matching Pursuit Decomposition-Based Signal Denoising to Detect and Quantify the Delamination of Sandwich Composites

Matching Pursuit Decomposition-Based Signal Denoising to Detect and Quantify the Delamination of Sandwich Composites

Experimental and numerical study of specific bending behavior of tufted multilayered reinforcements and effects of tufting density

The tufting technology enhances the delamination and impact resistance of composites. The presence of tufting yarns leads to a modification of the structure of the fabric, which affects the bending behavior of tufted reinforcements. Tufted reinforcements experience significant slippage during bending, challenging classical plate and shell theories. Therefore, the bending behavior of tufted reinforcement is investigated and a specific fibrous shell approach is proposed, assuming quasi-inextensibility of fibers and potential slippage between them. The influence of tufting yarns on the bending behavior is integrated into the constitutive model. The experimental results show that the bending stiffness of reinforcements can be increased by tufting density. The simulations exhibit a good agreement with experiments, demonstrating that the proposed approach can accurately capture not only the bending deflections of tufted reinforcements, but also the rotation of material direction indicators. Using the proposed numerical method, the prediction accuracy for deflection and rotation angle of tufted reinforcements reaches 90% in cantilever bending tests and 85% in three-point bending tests. These novel insights can deepen the understanding of the bending behavior of tufted reinforcements and be an asset of the developing numerical model for the forming simulation.

Composite delamination damage location based on non-orthogonal air-coupled ultrasonic guided waves and Artifact-Reduction damage index

This study focuses on the localization of delamination damage in composite materials. Due to the attenuation of the air-coupled ultrasound at the gas–solid coupling interface, the signal-to-noise ratio of the air-coupled ultrasonic signal is low, which results in low accuracy of damage detection. This paper proposes a method to locate delamination damage in composite materials. This method uses non-orthogonal Air-coupled Ultrasonic Guided Waves for B-scan; an artifact-reduction damage index (ARDI) is designed with the proportion of the scan paths containing damage information to the entire scan paths. These two exquisite designs improve detection accuracy. Finally, the probability of damage occurrence is calculated, and the detection of the damage location is achieved, with the positioning error of the damage being less than 1.5%.

Fabrication and comparison of interlaminar fracture toughness behaviour of glass epoxy composites with recycled milled Kevlar-carbon hybrid fillers

Current research uses a novel recycled milled carbon (rmCF), recycled milled Kevlar (rmKF), and innovative Hybrid fillers (rmHF) of both to increase glass/epoxy composite laminate delamination resistance. This study examines how crack propagation and fibre orientation affect laminated composite delamination fracture toughness. Recycled milled Fillers in the interlayer increase stiffness, delamination resistance, and fracture toughness by increasing the energy needed to crack the interlaminar domain. Here, Mode I, Mode II, and Mixed Mode (I/II) with GIGII = 25 %, 50 % and 75 % were studied for four different Interface fibre orientations. It appears [06/902/06] increased delamination toughness. Adding the novel recycled milled fillers improved delamination resistance. Among the three fillers, rmCF increased fracture toughness by 271 % and rmHF and rmKF composites had 220 % and 182 % higher fracture toughness. The synergy compensated for Kevlar's lower fracture toughness in the hybrid (rmHF). SEM analysis of fractured surfaces revealed crack deflection, individual debonding, and filler/matrix interlocking, all of which increase fracture toughness on different levels.

Increasing the Interlayer Fracture Toughness of Polymer Fabric Composites Using Local 3D-Reinforcement (Felting)

Introduction. One of the reasons for undesirable delamination of polymer composites with fabric reinforcement is low transverse shear properties. It is known that the reinforcement of polymer fabric composites in the Z direction reduces the sensitivity to delamination and increases the viscosity of interlayer fracture. Various methods of three-dimensional reinforcement of polymer fabric composites are proposed in the literature. However, they complicate the manufacturing process of the structure. The problem is solved by the method of three-dimensional reinforcement proposed in this article — felting. This is a local reinforcement of the composite in the Z direction with minimal production changes. The degree of Z-reinforcement is determined by the felting density, i.e., the number of needle punches per 1 cm2 of the fabric package. The work is aimed at evaluating the effect of felting on the interlayer crack resistance of a composite material.Materials and Methods. The interlayer fracture toughness GIIc was determined on a cross-woven fiberglass with felting of 10 cm-2. The material was impregnated with Etal-370 resin and Etal-45 hardener. Experiments according to ASTM D7905M–14 and GOST 33685–2015 standards were carried out on an Instron 5900R test machine. The stress state at the crack tip was analyzed with regard to the nonlocal strength theory in the ANSYS Workbench program (option “static strength analysis”). The finite element method (FEM) was used.Results. The “load — displacement” curves were considered for the samples. Values GIIc were calculated. The results of ENF tests for felting density of 0 cm–2 and 10 cm–2 were summarized. Control samples and felting samples were compared. In the latter case, GIIс turned out to be ~33% higher. The stress state at the crack tip was calculated under DCB and ENF loading. The dependences of maximum normal and shear stresses, as well as displacements, were visualized in the form of graphs and color charts. To get the calculated “load — displacement” dependences using FEM, the reverse method of obtaining transverse shear constants was used. DCB loading showed that felting provided increasing the rupture strength in the Z direction to ~18%, by 39 to 46 MPa, and in the planes XZ— to ~16%, by 77 to 89 MPa.Discussion and Conclusion. Felting as a method of local three-dimensional reinforcement enhances the interlayer crack resistance of polymer fabric composites. It provides reducing the area of stratifications after local impacts during the operation of structures. Flexible felting technology makes it possible to create zones with an arbitrary impact density, increasing fracture toughness only in the required places of structures. The FEM analysis of the stress state at the crack tip within the framework of the nonlocal strength theory has shown that in strength calculations, the stratification crack can be considered as a stress concentrator.

Dynamic data driven load-carrying capacity prediction method for composite laminates with delamination

The delamination of composites has invisibility and can reduce the load-carrying capacity (LCC) of structures. In this paper, a dynamic data driven LCC prediction method for composite laminates considering delamination is proposed. The method is divided into offline and online phases: In the offline phase, finite element modeling, prior information acquisition, and database construction are carried out. In the online phase, the Bayes factor is used to realize the rapid mapping between sensor data and the sample in the database to predict the LCC of the structure. In numerical cases with noise, the prediction errors of LCC are within 2.3% with sensor data, and the introduction of prior information can improve efficiency and accuracy of the prediction. The material parameters and delamination sizes of the identification results are the samples closest to the given solution in the database. In test cases, the information from strain arrays can effectively reflect the delamination growth of the laminate. After three times data assimilation, the prediction errors of LCC are within 10.5%.

An analytic solution for bending of multilayered structures with interlayer-slip

Layered structures are prevalent in both natural environments and engineered composite materials. The elastic bending behavior of these structures is primarily governed by properties of their abundant interfaces. While the behavior of two- and three-layered beams has been extensively studied, this research shifts the focus to the impact of elastic shearing at interfaces on the deflection of multilayered structures comprising a substantial number of layers. We present an analytical solution indicating that the bending properties of multilayered beams and plates are nonlinearly dependent on interfacial stiffness. Denoting Se as the effective bending stiffness of an n-layered beam of length L, and S0 as the bending stiffness of a perfectly bound counterpart, we arrive at SeS0=11+(n2−1)tanhαLαL where αL represents a dimensionless parameter related to geometry and material properties. The analytical solutions, validated through finite element simulations, highlight the substantial variations in stiffness across different layered structures. This solution could also be instrumental in assessing interfacial damage and delamination in lamellar composites.

NBR‐Rich Nanofibrous Membranes for Hindering Composite Delamination: Comparison of the Performance Obtained Using Liquid and Photocrosslinked Rubber

AbstractThis work compares the delamination behavior of epoxy CFRPs nano‐modified with nitrile butadiene rubber/polyethylene oxide (NBR/PEO) blend nanofibrous membranes with a rubber content of 70 wt%. While the electrospun mat is able to retain the nanofibrous structure even without crosslinking, photocrosslinking is also carried to evaluate the potential different efficacy on the delamination hindering. Double cantilever beam (DCB) and end‐notched flexure (ENF) tests show significant improvements of the energy release rates (G) both in Mode I (up to ≈4 times) and Mode II (up to ≈1.5 times). In particular, the presence of “liquid” rubber (uncrosslinked mat) leads to the best reinforcing action in Mode I, while the crosslinked membrane gives the highest delamination hindering in Mode II.

A new modified direct method for determining the mode I delamination traction-separation law

A new equation was developed for the crack-tip separation in the double cantilever beam (DCB) specimen, which has been standardised for mode I delamination of composites. The very simple closed-form equation is based on a pseudo-elastic beam model and on the effective crack concept. Moreover, it only requires the common load–displacement data up to crack initiation and easy to obtain elastic moduli. Strain-energy release rate versus crack-tip separation curves can then be differentiated for obtaining the tractions, as in the classical direct method. Numerical results for piecewise linear traction-separation laws (TSL) showed good accuracy of strain-energy release rate versus crack-tip separation curves predicted. Application to two carbon/epoxy materials gave very promising TSL results, including cohesive strengths similar to transverse tensile strengths and post-peak steep traction decreases.

Overcoming the cohesive zone limit in the modelling of composites delamination with TUBA cohesive elements

The wide adoption of composite structures in the aerospace industry requires reliable numerical methods to account for the effects of various damage mechanisms, including delamination. Cohesive elements are a versatile and physically representative way of modelling delamination. However, using their standard form which conforms to solid substrate elements, multiple elements are required in the narrow cohesive zone, thereby requiring an excessively fine mesh and hindering the applicability in practical scenarios. The present work focuses on the implementation and testing of triangular thin plate substrate elements and compatible cohesive elements, which satisfy C1-continuity in the domain. The improved regularity meets the continuity requirement coming from the Kirchhoff Plate Theory and the triangular shape allows for conformity to complex geometries. The overall model is validated for mode I delamination, the case with the smallest cohesive zone. Very accurate predictions of the limit load and crack propagation phase are achieved, using elements as large as 11 times the cohesive zone.

Fracture toughness resistance curves for a delamination in CFRP MD laminate composites, Part II: Mixed-mode deformation

The use of composite laminates continues to increase, especially in the aerospace industry, due to their high strength-to-weight ratio, resistance to corrosion, and surface degradation. However, in such materials, separation of plies, referred to as delamination, is common. Characterization of the driving forces causing delamination initiation and propagation is different in the case of mode I, mode II, or mixed-mode I/II deformations. This paper is Part II of a two-paper series. Results from calibrated end-loaded split specimens, producing nearly mode II deformation, were presented in Part I. Here, mixed-mode end-loaded split, quasi-static tests were performed. Two multi-directional carbon fiber reinforced polymer material systems are considered and are referred to as the ’wet-layup’ and ’prepreg’, which is attributed to their manufacturing process. Based upon results from three-dimensional finite element analyses in conjunction with the displacement extrapolation method, as well as with the conservative interaction energy or M-integral, stress intensity factors were determined. Based upon the obtained stress intensity factors, the in-plane and out-of-plane mode mixities were evaluated by means of phase angles as a function of the delamination extension through the specimen width. In addition, fracture toughness resistance curves, or R-curves, were generated as a function of delamination extension. The critical interface initiation and fracture resistance interface energy release rate values were determined based on the obtained stress intensity factors and compared with values obtained from the J-integral. Both methods are considered local. Additionally, the global experimental compliance method was employed.Differences of less than 4% for the prepreg and 12% for the wet-layup were observed between the results obtained using the global and local methods. Moreover, it was found that although the materials and interfaces tested are different, the average in-plane mode mixity, as measured by the in-plane phase angle, was found to range between 0.645 rad and 0.668 rad. This implies that the opening mode is dominant for these specimens. In addition, the critical values of the interface energy release rate for initiation Gic and steady state propagation Giss of the two materials were found to be relatively close although the failure mechanisms are not the same.

A method for modelling arbitrarily shaped delamination fronts with large and distorted elements

The simulation of delamination in layered composites is currently limited for large structures. Typically, the use of Cohesive Zone Modelling leads to a requirement of keeping the elements smaller than 1.0 mm. As an alternative, this article presents an Energy Release Rate-based cohesive method enabling the use of elements significantly larger (up to 5 mm). A novel algorithm is presented to use the Virtual Crack Closure Technique with distorted elements not aligned with the delamination front. When the propagation criterion is met, a cohesive law is introduced to model the progressive crack growth along the newly created crack surface, ensuring to dissipate the correct amount of energy. The method is validated for different propagation tests. Notably, Double Cantilever Beam and End-Notched Flexure tests are accurately modelled with large and distorted elements. Finally, a partially reinforced DCB test demonstrates the ability of the method in representing an evolving delamination front.

A Comparative Analysis on the Optimization of Carbon Fibre Reinforced Polymer and Glass Fiber Reinforced Polymers as Wrapping Structures on Defected Piping System using Computational Simulation Approach

This study examined the application of carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) as wrapping structures for defective pipe systems. The structural behavior and performance of the CFRP and GFRP wrapping structures were assessed using computational simulation methodologies. The goal of the study was to determine the best wrapping material for strengthening the integrity and reliability of piping systems with defects by comparing the results of the simulations. The study evaluated the capability of the proposed composite wrapping structure through CAD simulation. The simulations provided preliminary analysis and visually depicted deformations, aiding in the selection of an optimized lamination orientation for the composite wrapping structure in real-world applications. Eventually, this approach could have alleviated two primary failure modes that were common in composite repair: composite overloading due to excessive thickness and composite delamination from the substrate. The results of this study would have helped enhance effective and efficient pipe repair techniques in a variety of industries by offering useful insights into the selection and use of suitable wrapping structures for repairing defective pipes.

Quantitative assessment of delamination in composites using multiple local-defect-resonance modes

Accurately visualizing the geometry and dimensions of internal delamination in fiber-reinforced polymer (CFRP) composites is a challenging endeavor. In this paper, we develop a method to identify and characterize delamination in composites by the integration of multiple local defect resonance (LDR) modes. The proposed method was validated by using T300/M914 CFRP plates containing three distinct defect geometries, employing both numerical simulations and experimental measurements. The approach commences with the application of a frequency-domain finite element method for LDR frequency determination, emphasizing improved computational efficiency. This technique is further corroborated through the use of the defect-to-background ratio (DBR) method, which identifies LDR frequencies in both numerical simulations and experimental testing. The integration of multiple LDR modes (IMLDR) at various frequencies enables precise imaging of delamination defects of diverse geometries and sizes. Experimental results closely align with the numerical findings, confirming that the integrated imaging results accurately correspond to artificial defects. This method furnishes precise descriptions of damage location, geometry, and dimensions. The obtained results indicate that the proposed IMLDR-based technique significantly enhances the accuracy and reliability of delamination imaging in composites. Consequently, it offers an effective approach for quantitatively assessing delamination damage in composites.

Abrasive waterjet cutting of r‐GO infused magnesium fiber metal laminates: Experimental investigations and optimization through gorilla troops algorithm

AbstractLaminated metal‐composite structures, known as fiber metal laminates (FMLs), are modern lightweight materials extensively utilized in diverse industries such as aerospace and automotive manufacturing. These materials offer enhanced impact and fatigue resistance, making them invaluable for various applications. However, machining FMLs poses a challenge due to the occurrence of delamination and heterogenous in nature during conventional methods. Therefore, this study aims to investigate the quality characteristics such as kerf width, surface roughness and kerf taper of Magnesium based FMLs processed with an unconventional machining process namely abrasive water jet cutting (AWJC). These FMLs comprise alternately stacked kevlar/carbon fibers adhesively bonded with epoxy resin matrix filled with varying wt% of reduced graphene oxide (r‐GO), combined with AZ31B alloy sheet as the skin material. AWJC experiments were performed by varying the process parameters including waterjet pressure (275–325 MPa), stand‐off distance (2.5–3.5 mm), and cutting speed (600–800 mm/min) based on the box–behnken experimental design. The findings from the statistical analysis underscore the significant influences of stand‐off distance and waterjet pressure on kerf characteristics, while the inclusion of r‐GO is observed to notably affect the surface quality. In pursuit of enhancing cut quality, a multi‐response optimization was conducted employing the Gorilla Troops Optimization (GTO) algorithm. Comparative analysis with established metaheuristics like the gray wolf algorithm, dragonfly algorithm, and harmony search algorithm reveals GTO's superior performance across various metrics, including rapid convergence, diversity, and spacing values. Further, the cutting‐induced damages such as matrix plowing, fiber‐metal debonding and composite delamination were observed through microstructure analysis.Highlights Magnesium (AZ31B) fiber metal laminate comprising with various wt% of reduced graphene oxide was fabricated. Abrasive waterjet cutting of FMLs were performed based on box–behnken design experimental approach. Statistical analysis and influence of process parameters on the kerf width, surface roughness and kerf taper were investigated. Multi‐response optimization was carried out using metaheuristic‐based gorilla troops algorithm.

Effect of Layers on Delamination and Tensile Strength of Woven Fiber Composites with Polyester Matrix

A composite is a combination of 2 or more different materials. The composite joining process can use adhesives or mechanically by making holes. During the process of making holes in the composite, it can cause delamination in the composite. Delamination and layer thickness greatly influence the strength of hollow composite joints. This research aims to determine the effect of delamination factors and the number of layers on the tensile strength value of the composite. The materials used in this research are polyester resin and woven glass fiber. The method used is vacuum bagging with variations in the number of layers, namely 3 layers, 4 layers, 5 layers, and 6 layers. Tensile testing refers to ASTM D638 standards. Specimens that have been cut according to standards will then be perforated in the center with a hole diameter of 4 mm using a milling machine. The highest tensile strength value was obtained in the 6-layer variation of 237.448 MPa and the lowest value was obtained in the 3-layer variation of 186.221 MPa. The delamination value greatly influences the tensile strength of the composite, where the more layers, the delamination value will decrease and increase the tensile strength of the composite.

Mechanical and Ballistic Properties of Epoxy Composites Reinforced with Babassu Fibers (Attalea speciosa).

The mechanical and ballistic performance of epoxy matrix composites reinforced with 10, 20, and 30 vol.% of babassu fibers was investigated for the first time. The tests included tension, impact, and ballistic testing with 0.22 caliber ammunition. The results showed an improvement in tensile strength, elastic modulus, and elongation with the addition of babassu fiber, and the 30 vol.% composite stood out. Scanning electron microscopy analysis revealed the fracture modes of the composites, highlighting brittle fractures in the epoxy matrix, as well as other mechanisms such as fiber breakage and delamination in the fiber composites. Izod impact tests also showed improvement with increasing babassu fiber content. In ballistic tests, there was an increase in absorbed energy. All composites surpassed plain epoxy by over 3.5 times in ballistic energy absorption, underscoring the potential of babassu fiber in engineering and defense applications.

Design parameters affecting mechanical failure and electrochemical degradation of ultrathin Li-ion pouch cells under repeated flexing

Understanding mechanical failure modes of Li-ion battery electrodes of varying sizes and capacities is crucially important for the development of mechanically robust and high energy density flexible lithium-ion batteries (FLIBs). Three types of pouch cells (nominal capacities of 15, 25, and 50 mAh) were examined to understand how various design features used in the cells affected their mechanical failure modes and electrochemical performance after repeated introduction of compression and tension during bending. Postmortem microstructure analysis was carried out to identify the impacts of repeated flexing; several failure modes such as crack propagation, particle detachment, composite delamination, separator damage, electrode tears, and micro-short circuits were observed. We find that the observed mechanical failure modes are mainly dependent on the: 1) size and shape of the electrode composite materials, 2) configuration of the components within the cell (e.g., method of electrode folding, location of welded tabs), and 3) orientation of the long axis of the cell with respect to the bending axis. It was observed that the discharge capacity for all cell types studied herein was only slightly decreased (∼6–7% at 2C-rate) even after 3,000 repeated bends at a 25 mm radius of curvature provided if the bending axis is aligned to the long dimension of the cell. The results of this study provide valuable information on possible failure modes in Li-ion battery electrodes subjected to repeated flexing and how they can be mitigated to improve the dependability of practical pouch cells for FLIBs.

High temperature tribological response of Fe-2Cu-0.8C-CaF2 self-lubricating composites at high speeds

In this work, Fe-2Cu-0.8C-CaF2 self-lubricating composites with calcium fluoride solid lubricant (3 □ 12 wt.%) were examined for their friction and wear at 5 and 10 m/s, at 500 °C. Addition of CaF2 decreased density and hardness of composites. During sliding, materials gained weight due to oxidation. Compared to the base matrix (Fe-2Cu-0.8C), composites showed lower weight gain and lower coefficient of friction. Increase in porosity with CaF2 content increased oxidation resulting in higher weight gain and increased friction due to wear debris abrasion. Increase in speed reduced weight gain due to higher material loss. Adhesion was the dominant wear mechanism in base matrix; delamination and wear debris abrasion in composites. Temperature rise at sliding surfaces was theoretically estimated. Increase in speed increased temperature, which reduced friction due to softening and shearing of solid lubricant. Composite with 3 wt.% CaF2 showed least surface damage and 6 wt.% showed lowest coefficient of friction, i.e., lower by 16% and 10% at 5, 10 m/s than base matrix. Tribological response of the composites to a broad range of applied parameters, viz. speed, load and temperature taken from earlier works and present work is briefly summarized. The study suggests the dominant role of CaF2 content and the wear debris in altering the tribological response. Further, the stability of the developed composites at high temperature and high load conditions was also established. The study suggests that the developed composites could serve high-load and high-temperature applications for heavy machinery such as bearings, shafts and gears.